Flue stack outlet

ABSTRACT

The effective height of smoke stacks is increased to minimize ground level concentration of the effluents entrained or contained in the issuing gases by minimizing the entrainment of the cold ambient air into the issuing plume, by modifying the exit velocity distribution of the gases. The invention may comprise an external extension or an internal attachment to existing stacks or the stack may include the features of the invention when it is designed and built.

United States Patent 1191 Guelph June 18, 1974 FLUE STACK OUTLET 3,1 15,820 12/1963 [75] Inventor: Gee Tsang Guelph, Ontario, Canada v Primary Examiner-W1lham E. Wayner [73] Assgne'sZ Research Cm'lmratmn New York Assistant Examiner-William E. Tapolcai, Jr. Attorney, Agent, or FirmHarold L. Stowel] [22] Filed: Mar. 27, 1973 21 Appl. No; 345,472 [5711 ABSTRACT The effective height of smoke stacks is increased to 521 US. Cl. 98/58, 126/307 R minimize gmund level Concentration of the effluents 51 Int. Cl F231 17/02 entrained mmained the issuing gases by minimiz- Field of Search n 1. R lflg the entrainment Of the COM ambient air into the 126/307 issuing plume, by modifying the exit velocity distribution of the gases. The invention may comprise an ex- [56] References Cited ternal extension or an internal attachment to existing stacks or the stack may include the features of the in- UNITED STATES PATENTS vention when it is designed and built. 2,764,972 10/1956 Ryder 126/307 R 2,856,837 10/1958 Thulman 126/307 R 5 Claims, 3 Drawing Figures Adelt 98/60 1 FLUE STACK OUTLET BACKGROUND OF THE INVENTION To reduce air pollution in the lower atmosphere and to minimize ground level concentration of stack gas borne pollutants, higher and higher smoke stacks have been recently built. Further efforts have been made to increase the discharging velocity and temperature of the flue gases and thus increase the effective heights of the smoke stacks. However, the building of tall chimneys is expensive and the addition of momentum and heat to the flue gases also involves substantial additional operational cost. The current cost for building smoke stacks for power stations of about foot diameter is about 1,000.00 dollars/ft., so that increasing the height of chimneys is a very expensive operation.

THE PRESENT INVENTION By means of the present invention the effective height of smoke stacks is increased to minimize ground level concentration of the effluents entrained or contained in the issuing gases by minimizing the entrainment of the cold ambient air into the issuing plume, by modifying the exit velocity distribution of the gases. The invention may comprise an external extension or an internal attachment to existing stacks or the stack may include the features of the invention when it is designed and built.

The hot effluents from industrial chimneys rise into the atmosphere because of their momentum and buoyancy. It has been found that as a hot plume rises, ambient air is entrained into the plume and the entrained air increases the upward mass flux of the plume and reduces the plume velocity and temperature excess. The reduction in temperature excess in turn reduces the subsequent velocity increase caused by buoyancy.

To reduce the ground level concentration of the effluents, it is desirable to have the effluents to rise to a high altitude. Besides increasing the stack height and increasing the exit velocity and temperature, it has been found a higher altitude may also be reached by better preserving the velocity and temperature excess of the plume. As the temperature and velocity of a plume are reduced by ambient entrainment, the temperature excess and velocity of a plume will be best preserved if the ambient entrainment is reduced to minimum.

Entrainment of fluid between two flow layers occurs when the two layers flow at different velocities. Ambient air is entrained into a plume because the. vertical velocity of the plume and the ambient air are different. The greater is the velocity difference, the greater will be the entrainment.

By changing the conventional generally uniform velocity distribution in the exit gases of a stack to provide a velocity distribution such that instead of having the ambient air entrained by the hot plume, the plume entrains also hot gases from the chimney the flue gases will not be diluted and the temperature and velocity of the plume will be better preserved. The above may be achieved by making the flue gases flowing out from the chimney in concentric layers of progressively decreasing velocities from the center to the edge. The central layer will then entrain fluid from the layer next to it, which in turn will entrain fluid from the layer further out. In such a fashion each layer entrains fluid from the outer layer until the edge of the chimney is reached.

The theory of this discovery is set forth in my paper, Stack Exit Velocity Distribution for Higher Effective Stack Height, MS. NO. 580, Atmospheric Environment; Pergamon Press, Vol. 6. November 1972.

In general the objects and advantages of this invention are provided by a flue stack outlet for increasing the effective height of a smoke stack by minimizing the entrainment of the cold ambient air into the issuing plume comprising a plurality of concentric cylindrical sleeves mounted at the exit outlet of the stack, said sleeves modifying the uniform velocity distribution of the gases in the stack into a velocity distribution in the form of a cone with the highest velocity at the center and the velocities decreasing radially outwardly therefrom.

The invention will be more particularly described in reference to the accompanying drawings wherein:

FIG. 1 is a fragmentary sectional view through an attachment to a flue stack constructed in accordance with the present invention and diagrammatically illustrating the velocity distribution at the upper end of the stack;

FIG. 2 is a section substantially on line 2--2 of FIG. 1; and

FIG. 3 is a fragmentary sectional view similar to that illustrated in FIG. 1 of a modified form of the present invention also diagrammatically illustrating the velocity distribution at the upper end of the stack attachment.

Referring to FIGS. 1 and 2, 10 generally designates an attachment for the upper end of a conventional flue or stack 12 having a diameter D of about 10 feet. The attachment 10 includes a plurality of relatively thin metal, fiber glass or the like cylindrical dividers desig nated 14, l6, l8 and 20 which divide the gases issuing from the stack 12 into gas streams 22, 24, 26, 28 and 30. The internal diameter of the attachment 10, at its uppermost end 32, is approximately 1.3 times D.

The lower end 34 of the attachment 10 is provided with suitable means for securing the attachment to an existing stack and the height of the attachment is approximately l to 2 times the diameter D of the stack 12. Each of the cylindrical dividers l4, l6, l8 and 20 is shaped so that the velocity distribution of the gases issuing from the upper end of the attachment generally follows the diagrammatic illustration designated 36 at the end of the stack and that the pressure distribution is laterally uniform. From the velocity distribution diagram it will be seen that the highest velocity is provided for the gases issuing from channel 22, the next lower from channel 24, the next lower from channel 26, etc. to the lowest velocity gases issuing from the outermost channel 30 thus presenting to the ambient atmosphere the coolest and the lowest velocity gases. The velocity distribution curve designated 38 is an ideal curve for velocity distribution if an infinite number of cylindrical dividers could be provided in the stack; whereas using four dividers an approximation of said preferred velocity gradient is obtained.

Each of the cylindrical dividers 14 through 20 is maintained in the illustrated position by spiders or webs generally designated 40, 42, 44 and 46 for gas flow channels 24, 26, 28 and 30 respectively. As hereinbefore set forth the number of concentric cylinders or rings employed in the construction of the gas velocity modifying attachment of the invention is not critical; however it has been found that in general a gas velocity distribution approaching the ideal would require about four or live in number for a stack feet in diameter. However as few as two gas channels will provide useful results and therefor from 2 to 10 channels would be a useful range. Further the height of the sleeve or attachment is not particularly critical as long as the gases flowing through the concentric passages have sufficient time to attain the desired velocity from the generally uniform gas velocity issuing at the upper end of the stack. In general it has been found that the desired velocity will be attained by the gases when the channels are from about one to about two times the stack diameter.

The spacing and the configuration of the passages 22 through 30, formed by the cylindrical dividers 14 through 20, are determined, for a particular installation, by the diameter of the stack and the volumetric flux and momentum flux of normal gas flow through the stack to provide laterally uniform pressure distribution at the exit and non-separation in the channels.

The velocity distribution at the stack for a plume of minimum ambient entrainment is determined from the following equation:

where (b is the velocity of flow in a channel at the top of the attachment divided by the velocity at the center channel at the outlet and r: is the ratio of the radius of the selected channel to the radius of the entire device at its top.

Further an angle of from about 3 to about 8 for the upwardly enlarging channels between two adjacent cylindrical dividers would provide separation-free flows.

In FIG. 1 of the drawing the velocity distribution is obtained by providing channel 22 with a large inlet area than outlet area, channel 24 with about uniform spacing at the top and at the bottom, while channels 26, 28, and 30 have reduced inlet ends and enlarged outlet ends.

At low gas velocities the top of the attachment may include an annular collar, not shown, which collar may have a width as large as about half the diameter of the chimney. such collar minimizes the effect of the wake of the chimney in pulling the plume down into the wake.

Further as hereinbefore described the advantages of the invention are obtainable by mounting the attachment partially or wholly within the confines of an existing or a new stack 12. Where the attachment is external or internal diameter ratios between the internal diameter of the attachment and the stack of about l.2D to about 1.35D provide satisfactory results.

Employing the concentric ring attachment 10 having a height of about feet as shown in FIG. 1 of the drawing, on a stack having an internal diameter of about 10 feet results in a plume rise to an altitude of at least about 50 feet higher than that of the same stack without the velocity changing attachment at a cross wind velocity of 7 mph. This means an increase of the effective height of the smoke stack by 50 feet and with the current cost of building smoke stacks of about 1,000.00 dollars per foot, a net savings of approximately about 45,000.00 dollars is realized when the additional cost of making the attachment is about 5,000.00 dollars.

Referring now to FIG. 3 of the drawing, a modified form of the present invention is shown wherein the stack attachment includes a low velocity air jacket. In the drawing designates a plume modifying attachment to a stack 12'. The attachment 100 comprises an outer shell 102 and a pair of cylindrical dividers 104 and 106 which divide the attachment into three concentric gas fiow paths 108, 110 and 112 each having gas flow velocities as indicated by the velocity vectors V at the upper end of the drawing. Associated with the attachment is an outer cylindrical sleeve 114 which provides a low velocity air jacket for the gas plume. The jacket or sleeve 114 terminates at edge 116 above the lower end 118 of the attachment and a curved deflector plate 120 is provided at said lower end to assist in directing the crosswind indicated by directional arrow C into the low velocity air jacket. Such an air jacket surrounds the gas plume with a jacket of upwardly moving air which will reduce entrainment of the surrounding air in the outer portions of the plume and is particularly useful where there are crosswinds which affect the rise of a gas plume from a chimney. In other respects the flue extension or flue outlet means of FIG. 3 is similar to that illustrated in FIGS. 1 and 2 of the drawing.

F rom-the foregoing description it will be seen that the present invention fully accomplishes the aims and objects set forth herein.

I claim:

1. A flue stack outlet for increasing the effective height of a smoke stack by minimizing the entrainment of the cold ambient air into the issuing plume comprising a plurality of concentric cylindrical sleeves mounted at the exit outlet of the stack, the inlet ends of all of the concentric channels formed by said sleeves being in direct communication with the stack outlet and the outlet ends of said channels being in direct communication with the ambient air, each channel so varying in cross-sectional area between its inlet and outlet ends as to modify the uniform velocity distribution of the gases in the stack into a velocity distribution in the form of a cone with the highest velocity at the center and the velocities decreasing radially outwardly therefrom.

2. The invention defined in claim 1 wherein the velocity modifying channels have a diffusing angle of from 3 to 8 between adjacent cylindrical sleeves.

3. The invention defined in claim 1 wherein there are from 3 to 5 concentric cylindrical sleeves.

4. The invention defined in claim 3 wherein the length of the cylindrical sleeves is from 1 to 2 times the diameter of the stack.

5. The invention defined in claim 3 further including a low velocity air jacket about the outermost of said concentric cylindrical sleeves.

UNITED STATES PATENT OFFICE CERWMCATE 0F CORRECTION Patent No. 3 a 817 ,1 62 Dated June 1 1974 G Inventor(s) ee Tsang It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[75] Inventor: Gee Tsang, Guelph, Ontario, Canada Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

MCCOY GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents -'ORM PO-1050 (10'69) USCOMIMDC 50376P69 U S GOVIRNMENT PR'N ING OFFICE 59 93 o 

1. A flue stack outlet for increasing the effective height of a smoke stack by minimizing the entrainment of the cold ambient air into the issuing plume comprising a plurality of concentric cylindrical sleeves mounted at the exit outlet of the stack, the inlet ends of all of the concentric channels formed by said sleeves being in direct communication with the stack outlet and the outlet ends of said channels being in direct communication with the ambient air, each channel so varying in cross-sectional area between its inlet and outlet ends as to modify the uniform velocity distribution of the gases in the stack into a velocity distribution in the form of a cone with the highest velocity at the center and the velocities decreasing radially outwardly therefrom.
 2. The invention defined in claim 1 wherein the velocity modifying channels have a diffusing angle of from 3* to 8* between adjacent cylindrical sleeves.
 3. The invention defined in claim 1 wherein there are from 3 to 5 concentric cylindrical sleeves.
 4. The invention defined in claim 3 wherein the length of the cylindrical sleeves is from 1 to 2 times the diameter of the stack.
 5. The invention defined in claim 3 further including a low velocity air jacket about the outermost of said concentric cylindrical sleeves. 